1. Field of the Invention
The present invention relates to two-wheel drive and four-wheel drive transfer devices for shifting between two and four-wheel drive in vehicle equipped for such operation and to control devices for four-wheel steering mechanisms and related devices.
2. Description of the Prior Art
Two and four-wheel drive transfer devices for fourwheel drive vehicles are disclosed, for example, in Japanese patent Application No. 61-229542. FIG. 2 shows such a prior device and includes a shaft 1 which receives a drive torque from an engine through a transmission and rotates as a front or rear wheel drive shaft. An output shaft 3, which acts as a front wheel drive shaft, is supported in the shaft 1 by means of a bearing arrangement 2. The shaft 1 has a spline set 4. The output shaft 3 is provided with a spline set indicated at reference numeral 7. A sliding dog clutch 5 is movable by a shift fork 6 between a first or illustrated position in which the sliding dog clutch 5 is only in engagement with the spline set 4 and a second position for connecting spline sets 4 and 7 for concurrent rotation. In the first position of operation, the transfer mechanism provides for two-wheel drive operation. A second position of the sliding dog clutch 5 provides for engagement between the spline set 4 of the shaft 1 and the spline set 7 of the shaft 3. When the sliding dog clutch 5 is in such position as to interconnect the spline sets 4 and 7, four-wheel drive operation would then be available for the vehicle.
A worm gear 10 is secured or otherwise attached to a motor shaft 9 and rotates therewith at the speed as driven by the motor, for example, a high speed electric motor drive. A worm wheel or gear 11 is in engagement with the worm gear 10 and is supported on and relatively rotatable with an output shaft 12 through a sleeve arrangement 13. Two rotating plates 15a and 15b are provided on the output shaft 12 so as to co-rotate with the worm wheel 11. The plates 15a and 15b are integrated or interconnected by means of a connecting sleeve 14. The output shaft 12 is also provided with two plates 16a and 16b which are secured thereto so as to permit the transmission of the rotary driving force from the worm gear 11, through plates 15a and 15b to the plates 16a and 16b. Positioned between the rotating plates 15a and 15b are two split spring guides 17a and 17b. A tension spring 18 is inserted between the spring guides. The tension spring 18 is provided with end portions 19a and 19b. The end portion 19a of the spring 18 is in contact or otherwise connected with the plates 15b and 16b. The end portion 19b of the spring 18 is in contact or otherwise connected with the plates 15a and 16a.
A conductive, e.g., copper, contact plate 22 is provided on the worm wheel 11 so a to rotate therewith. An opposing contact is provided on the casing 21. The plate and contact cooperate so as to provide an indication of the rotational position of the worm wheel. A projection 24 is provided so as to surround and protect a cam switch 23 actuatable by movement or rotation of the worm wheel. Gear 25, of relatively small diameter, is secured to the output shaft 12 and is in meshing engagement with gear 26, of larger diameter, secured or fixed to countershaft 27. The countershaft 27, in a manner similar to shaft 12, is rotatably secured in the casing 21. The counter shaft 27 is also provided with a pinion gear 28 which is connected to an output shaft 29. The connection between the gear 28 and output shaft 29 is through a rack and pinion arrangement (not shown). The output shaft 29 is arranged, with respect to the drive gear 28, to provide a reciprocating motion. The output shaft 29 is secured to the fork shaft 30 on which the shift fork 6 is secured or fixed.
When the drive motor (not shown) is in operation and the sliding dog clutch 5 is in engagement with the spline set 4, the worm gear 10 is rotated by the motor shaft 9 and the worm wheel 11 is rotatably driven thereby. The rotational movement of the worm wheel is transmitted to the rotating plate 15a so as to twist the end 19b of the torsion spring 18 so that the rotational torque of the worm wheel 11 is stored in the torsion spring 18. Due to the connection of the spring 18 to the plates 16a and 16b, the rotational torque is then transmitted through the plates 16a and 16b to the output shaft 12 so as to cause the output shaft 12 to rotate. Rotational movement of the shaft 12 rotates pinion gear 25 secured thereto and gear 26 which is in meshing engagement with gear 25 and which is secured to countershaft 27. The rotational movement of the countershaft 27 provides a reciprocating motion to the shaft 29 due to the driving engagement of pinion 28 with the shaft 29. Shaft 29 is then moved in a reciprocating direction. Upon movement of the shaft 29, the shaft 30, secured thereto, will follow so as to move the sliding dog clutch 5 to a position which engages the spline set 7 provided on shaft 3 while continuing to be engaged with spline set 4. The output shaft 3 is then connected to the shaft 1 so that four-wheel drive is obtained.
In the description of the above-discussed prior device, the engagement operation between splines 4 and 7 and the disengagement operation between the spline sets 4 and 7 is based upon the output of the torsion spring 18. Accordingly, it may be difficult to properly complete the operations of engagement and disengagement as the output requirement for movement of the shift fork differs for selecting between two-wheel and four-wheel driving conditions and will generate different ranges of noise and shock with each of the engagement and disengagement operations.